Honeycomb extrusion die

ABSTRACT

The invention discloses method and apparatus for providing a desired batch flow through desired regions of an extrusion die for forming honeycomb structures, and more particularly to the enhancement of batch flow in the skin-forming region of the die so as to provide a bounding wall of desired thickness and strength about a honeycomb core. Unlike prior methods, a recess or trough of desired depth and width is formed in a desired region of the inlet face of the honeycomb die, which reduces the pressure required to flow batch material through the die in such region. Such reduced pressure requirement translates in an increased flow rate in such region under constant extrusion pressure. Thus by increasing the flow rate through a honeycomb extrusion die in an outer peripheral region of flow in this manner, improved skin formation around a honeycomb core is obtained during the forming process.

This application claims the benefit of U.S. Provisional Application No.60/628,898, filed Nov. 17, 2004, by J. Rector.

BACKGROUND OF THE INVENTION

Honeycomb extrusion dies are commonly used to form cellular or honeycombceramic substrates for use in catalytic converters, which are utilizedin exhaust systems of internal combustion engines. In order to reduceback pressure within the exhaust system, it is necessary that the cellwalls or webs of the substrate have a substantially thin cross-sectionaldimension so as to provide a substantially large open frontal area.However, the thin walled structure must be protected so as to withstandnormal automotive impact requirements. One way to protect the inner cellwalls is to provide an outer skin of increased thickness, thus providingadditional strength to withstand external loads.

The present invention relates to honeycomb die designs, and moreparticularly to die designs offering improved control over the deliveryof plasticized powdered ceramic batch materials toward the skin-formingregions of such dies, in order to better control the thicknesses andflow properties of the co-extruded skin layers needed to effectivelysurround and protect the honeycomb core portions of the extrudedhoneycomb structures.

Current methods of providing a sufficient flow of skin-forming ceramicmaterial on extruded ceramic honeycombs have involved modifications ofthe pin or outlet side of the extrusion die. Generally, such methodscomprise the cutting away of material from the pin side of the dieand/or attaching throttling plates to the inlet side of the die bodiesto provide a thick, smooth skin area on the extruded part. U.S. Pat.Nos. 5,219,509 to Cocchetto et al and 6,455,124 B1 to Beall et al arerepresentative of such methods. Also U.S. Pat. No. 4,915,612 to Gangemeet al utilizes a mask associated with the discharge face of the die anda forming plate positioned on the inlet face of the feed holes toproduce an outer skin on a honeycomb substrate.

However, many of these know methods are subject to various handling andextrusion problems, including damaging the die pins during the cuttingaway process which renders the die completely useless. Partial pins,formed by a square cell pattern when being cut by a rounded skinpattern, are subject to excessive wearing. Also, the cutting of the pinsurface results in a variable surface finish on the completed die, whichproduces changing extrudate flow rates as the die is slowly eroded bythe flow of abrasive batch through the die. Also of concern arevariations in flow from one die to the next, which can cause highvariability in selects between dies and therefore reduced materialutilization in the forming plants. Further, where such variations inflow exist, the ceramic skins are not always well adhered to thehoneycomb core portions of the extruded parts.

It is known to increase the flow of skin-forming material by wideningthe discharge slots in the outer skin-forming region to improve the wetstrength of the formed part and to provide improved adherence of theskin on the ceramic honeycomb part. Such widening techniques, however,are expensive in terms of tooling and machine time. Further, thenecessary machining is irreversible. That is, the die cannot bere-converted to a uniform slot width design, which may be necessary dueto surface finish wear that eventually results in excessive flow ofbatch material in the skin-forming region.

SUMMARY OF THE INVENTION

The present invention relates to novel die designs wherein diemodifications effective to provide skin-forming and other flow controlenhancements involve the removal of die material from the batch inlet orfeedhole side of the extrusion die. Such modifications may be used aloneor in combination with current slot-modification technics, typicallyemployed at the pin or outlet side of the die. The removal of materialfrom the feedhole side of the die produces a shallow trough or recesswhich reduces the pressure required to flow extrudate through the die insuch area. The reduced pressure requirement translates in an increasedflow rate in such area under constant extrusion pressure. Thus thisinvention provides an improved manner to increase flow through ahoneycomb extrusion die in an outer peripheral region of flow which isutilized to create a skin around the honeycomb substrate during theforming process, while under constant extrusion pressure.

The removal of die material from the feedhole side of the extrusion diein the skin-forming region utilizes the basic physics of batch flowthrough the die, to improve and control extrudate flow in and adjacentto that region. In view of the fact that the length of the feed holeimpacts the extrusion pressure, by varying the feedhole length, theamount of wall drag experienced by the extrusion material in the feedholes can be controlled, resulting in increased batch flow through thosefeedholes which are formed shorter than adjacent feedholes. A desiredfeedhole length for improving flow to the skin-forming portion of thedie may be conveniently obtained by cutting a shallow trough or recessin the batch inlet or feedhole side of the die, in a narrow portion ofthe skin-forming region. Also, the conventional pin side modificationsmay be made to the die.

The extent of enhancement of batch flow through the skin-forming regionof the die is easily controlled by varying the depth and shape of thetrough formed in the inlet surface of the die. Further, the width of thetrough can be varied about the central axis of the die to adjust forinconsistencies in radial flow existent in various extrusion equipment.

A particular advantage obtained by utilizing a trough or recess on theinlet side of a honeycomb extrusion die to control the flow ofskin-forming batch is that when the trough is no longer necessary toprovide the enhanced flow to the skin-forming region, the inlet face ofthe die may be machined smooth to remove the trough and the die reused.Also, the inlet face may be machined to provide a different inlet faceconfiguration, which may be useful in controlling batch feed through theskin-forming and adjacent portions of the extrusion die for a differentpurpose.

It thus has been an object of the present invention to provide novelmethod and apparatus for controlling the flow of skin-forming batchmaterial through an extrusion die so as to improve the formation of abounding skin about a honeycomb core.

A further object of the invention has been to provide a honeycombextrusion die having a recess in its feedhole face for facilitating thecontrol of flow of batch material to a skin-forming region of the die,wherein the feedhole face may be re-machined and reused.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a prior art extrusion die.

FIG. 2 is a schematic cross-sectional view of an extrusion die embodyingthe present invention.

FIG. 3 is a schematic cross-sectional view of a further embodiment ofthe invention.

FIG. 4 is a view of the inlet or feedhole side of a die embodying thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to the drawings, FIG. 1 illustrates a prior art extrusiondie wherein a portion of the outlet pin face is cut away. The die 10 hasan inlet or feedhole face 12 open to a plurality of feedholes 14 and anoutlet or pin face 16 having a plurality of pins 18 surrounded bydischarge slots 20. A portion of the outlet face 16, adjacent an outerskin-forming region, is cut away at 22. A mask or skin-forming ring 24,spaced from the die 10 by a shim 26, overlies the cut away portion 22.The ring or mask 24 forms a reservoir 28 in the cut away portion 22,between the mask and the die, which is fed with batch material from feedholes 30 and reduced slots 32, when plasticized batch material (notshown) is caused to flow in the direction of arrow A. The materialcollected in reservoir 28 flows out through a skin-forming gap 34 as askin layer on a honeycomb core concurrently formed from plasticizedbatch material that is discharged from slots 20 not covered byskin-forming ring 24.

In order to modify the thickness of the skin and/or the web structureexiting the die, it is conventional to modify the widths of selectedslots, such as slots 32 and/or modify the width of the skin-forming gap34. Generally such openings are enlarged to locally increase batch flowin such areas. However, as noted above, such modifications areirreversible and therefore when the dies are so modified, once worn,they cannot be reconditioned for further use.

FIG. 2 illustrates a die 110, similar to die 10, but modified inaccordance with the present invention. As shown, a recess or trough 136is formed in the inlet or feedhole face 112 of the die 110 within theskin-forming region of the die. Material removal to form the trough 136may be effected by any suitable means, however, plunge electricaldischarge machining (EDM) produces a preferred burr-free method ofmaterial removal. The trough 136 is in communication with selectedskin-forming feedholes 140, and accordingly reduces the longitudinalextent of such feedholes. It thus is apparent that due to the recess ortrough 136 formed in the inlet face 112, the longitudinal extent offeedholes 140 is shorter than that of adjacent feedholes 130.Accordingly, wall drag on batch material flowing through shortenedfeedholes 140 is proportionately reduced with respect to that instandard feedholes 130, and thus batch flow through such shortenedfeedholes is increased and greater than that flowing through standardholes 130, so as to provide a controlled flow of skin-forming batchmaterial. The depth and/or the radial extent of the trough 136 can bevaried so as to adjust the increase of extrudate flow through theshortened feed holes 140 to a predetermined level as may be desired forthe thickness of the bounding skin to be formed about the honeycomb coresimultaneously formed by the die 110.

For even further control of batch flow rates through a honeycombextrusion die, the shape and depth of the trough may be varied in theradial direction, and/or the width of the recess may be varied about theperiphery of the die. FIG. 3 shows a further embodiment of the inventionwherein die 10 is modified by forming a recess or trough 236 of variablecross-section in the inlet or feedhole face 212 to form an improvedbatch flow control die 210. The variably shaped cross-section andpreselected width and depth of recess 236 are functions of radiallocation about the central longitudinal axis through the die and thedesired radius from such axis. This complex shape of trough 236including slanted wall 238 provides the ability to transition the flowof batch material from the thinner inner webs of the honeycomb core tothicker or heavier outer webs adjacent the peripheral wall where theactual skin region is joined.

To illustrate the controlled varied flow of batch material throughextrusion die 210, shortened feedhole 240 at the innermost extent ofrecess 236 will have the least amount of batch wall drag and accordinglywill facilitate the best flow rate through the die for providing adesired skin thickness. Feedhole 234, which is shortened by an innerlower end of slant wall 238, will produce a batch flow rate slightlyless than that of feed hole 240, but more than that provided by feedhole232 at an outer upper end of slant wall 238. Finally, standard feedholes230 will produce the most wall drag on the batch flow and accordinglywill have the least amount of flow rate to the discharge end of the die210. Since the flow rate of the batch is directly proportional to theweb thickness produced by the die, it can be seen that the slant wall238 gradually increases the web thickness toward the periphery of theextruded honeycomb structure and that the inner surface of the recess236 facilitates the production of a bounding skin of desired thickness.

Referring now to FIG. 4, the inlet or feedhole side of an extrusion dieis shown having an annular recess or trough which is provided with avariable depth D and width W around its extent with respect to angle Yto provide an adjustment to batch flow depending on local equipment flowvariation. For example, some extrusion systems may generate more or lessflow pressures against the extrusion die as a function of the radialangle Y, depending on the hardware employed. Further, as shown, thedepth D of the trough may also be varied as a function of radius R togenerate a taper or slant wall into and /or out of the cutout area. Thevariable wall provides for a smooth transition from the internal portionof the die to the recessed area and then back to face of the dieadjacent the skin area.

As previously noted, the inlet face modifications of the presentinvention may be utilized alone or in combination with other knownskin-forming measures.

Although the now preferred die configurations of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications may be made thereto without departing from thespirit and scope thereof as defined in the appended claims.

1. A method of controlling the flow of batch material in a desiredregion through a honeycomb extrusion die having an inlet facecommunicating with feedholes and an outlet face communicating withdischarge slots which comprises: forming a recess in the inlet face ofthe extrusion die in communication with feedholes within the desiredregion, and flowing batch material under pressure to said inlet face andinto said recess and all of the feedholes communicating with said inletface to provide a desired flow rate of batch material through thosefeedholes communicating with said recess.
 2. A method of controlling theflow of batch material in a desired region through a honeycomb extrusiondie having an inlet face communicating with feedholes and an outlet facecommunicating with discharge slots as defined in claim 1, including thestep of: machining the recess in the inlet face of the extrusion diewith a variable depth relative to the surface of said inlet face.
 3. Amethod of controlling the flow of batch material in a desired regionthrough a honeycomb extrusion die having an inlet face communicatingwith feedholes and an outlet face communicating with discharge slots asdefined in claim 1, including the step of: controlling the flow or batchmaterial through those feedholes within the desired region by varyingthe depth of the recess formed in the inlet face.
 4. A method ofcontrolling the flow of batch material in a desired region through ahoneycomb extrusion die having an inlet face communicating withfeedholes and an outlet face communicating with discharge slots asdefined in claim 1, including the step of: shortening the longitudinallength of those feedholes communicating with the recess formed in theinlet face and thereby reducing the amount of wall drag experienced bythe batch material flowing through such shortened feedholes as comparedto wall drag of batch material flowing through those feedholes notwithin the desired region.
 5. A method of controlling the flow of batchmaterial in a desired region through a honeycomb extrusion die having aninlet face communicating with feedholes and an outlet face communicatingwith discharge slots as defined in claim 4, including the steps of:flowing batch material under constant pressure to the inlet face of theextrusion die, and increasing the flow rate of batch material throughthe shortened feedholes relative to the flow rate of batch material inthose feedholes not within the desired region.
 6. A method ofcontrolling the flow of batch material in a desired region through ahoneycomb extrusion die having an inlet face communicating withfeedholes and an outlet face communicating with discharge slots asdefined in claim 1, including the steps of: forming the recess in anouter peripheral region of the honeycomb die and shortening thelongitudinal extent of the feedholes communicating with the recess,increasing the flow of batch material through the honeycomb extrusiondie in the outer peripheral region, forming a skin of desired thicknessaround an extruded honeycomb core with the increased peripheral flow ofextruded batch material, and maintaining the batch flow to the inletface under constant pressure.
 7. A method of controlling the flow ofbatch material in a desired region through a honeycomb extrusion diehaving an inlet face communicating with feedholes and an outlet facecommunicating with discharge slots as defined in claim 1, including thesteps of: machining the inlet face to remove the recess, and forminganother recess configuration in said inlet face.
 8. A method ofcontrolling the flow of batch material in a desired region through ahoneycomb extrusion die having an inlet face communicating withfeedholes and an outlet face communicating with discharge slots asdefined in claim 1, including the steps of: forming the recess in theshape of a trough in a narrow portion of the skin-forming region of thedie, and controlling the batch flow through the skin-forming region ofthe die by varying the depth and shape of the trough so formed in theinlet face of the extrusion die.
 9. A method of controlling the flow ofbatch material in a desired region through a honeycomb extrusion diehaving an inlet face communicating with feedholes and an outlet facecommunicating with discharge slots as defined in claim 1, including thesteps of: forming the recess in the form of a trough that varies indepth D about the die as a function of both a radial angle Y and aradius R, and providing the recess with a variable width W also as afunction of the angle Y.
 10. A method of controlling the flow ofskin-forming batch material through a honeycomb extrusion die, having aninlet face in communication with feedholes and an outlet face incommunication with discharge slots, so as to control and improve theformation of a bounding skin about an extruded honeycomb core, whichcomprises, forming a trough about a central axis of the die of apredetermined depth in the inlet face of the honeycomb extrusion die andwithin a narrow portion of a peripheral skin-forming region of the die,shortening the longitudinal length of the feedholes in the outlet facewhich are in communication with the trough, flowing batch material underconstant pressure to the inlet face of said extrusion die and into thefeedholes communicating with said inlet face, increasing the flow rateof batch material flowing through the shortened feedholes relative tothe remaining feedholes, and forming a skin of desired wall thickness ona honeycomb core with the batch material delivered to form such skin atan increased flow rate through the shortened feedholes.
 11. An extrusiondie for controlling and improving the formation of a bounding skin abouta honeycomb core which comprises, an extrusion die for forming honeycombsubstrates having an inlet face and an opposite outlet face, a pluralityof longitudinal extending feed holes communicating at one end with saidinlet face and at an opposite end with a plurality of discharge slotsformed in said outlet face, and recess means formed in the inlet face ofsaid extrusion die in communication with a desired region of feedholesfor reducing the pressure required to flow batch material through theextrusion die in said desired region and for providing a desired flowrate of such batch material through said region.
 12. An extrusion diefor controlling and improving the formation of a bounding skin about ahoneycomb core as defined in claim 11 wherein the longitudinal extent ofthe feedholes within said desired region is shorter than thelongitudinal extent of the remaining feedholes.
 13. An extrusion die forcontrolling and improving the formation of a bounding skin about ahoneycomb core as defined in claim 11, wherein said desired region is inan outer peripheral skin-forming region of said extrusion die.
 14. Anextrusion die for controlling and improving the formation of a boundingskin about a honeycomb core as defined in claim 11, wherein said recessmeans is of a constant depth from the surface of said inlet face.
 15. Anextrusion die for controlling and improving the formation of a boundingskin about a honeycomb core as defined in claim 11, wherein said recessis in the form of a variable depth recess means for controlling the flowrates of batch material flowing through the various feedholescommunicating with said variable depth recess means.
 16. An extrusiondie for controlling and improving the formation of a bounding skin abouta honeycomb core as defined in claim 11, wherein said recess means is inthe form of trough means of desired depth and width for controlling theflow rate of batch material through each feedhole communicating withsaid trough means.
 17. An extrusion die for controlling and improvingthe formation of a bounding skin about a honeycomb core as defined inclaim 11 wherein the recess means is in the form of trough means thatvaries in at least one of depth D, width W, and distance R from thecenter of the die as a function of a radial angle Y around the center ofthe die.